Balanced demand valve



Spt. 26, 1967v Y w. J. c ARTER, JR 3,343,563

BALANCED DEMAND VALVE Filed April 24, 1965 Unted States Patent O 3,343,563 BALANCE!) DEMAND VALVE William James Carter, Jr., Williamsville, N.Y., assigner to The Firewel Company, Inc., Bualo, N.Y., a corporation of Ohio Filed Apr. 24, 1963, Ser. No. 275,444 1 Claim. (Cl. 137-517) This invention relates to a demand valve, that is, a highly sensitive pressure reducing -valve responsive to pressure variations caused by the inhalations of the use-r to supply him with oxygen from a high pressure source at a pressure suited to his 'breathing requirements, such demand valves being particularly necessary in high altitude flying.

One of the principal objects of the invention is to provide such a demand valve which is very small and can, in fact, be inserted directly -in the oxygen supply line to the aviators mask, a demand valve for such respiratory purposes being in the form of a plain cylinder as short as one inch and having an outside diameter of .312 inch.

Another object is to provide such a demand valve which is light in weight, the demand valve illustrated, when made of stainless steel, weighing approximately one-half ounce.

Another principal object is to provide such a demand valve which is highly sensitive in Opening and closing in response to slight variations in outlet pressure as caused by the inhalations `of the user, such sensitivity lbeing achieved by using the full maximum cross sectional size of the spool of the valve as the surface of the valve head and which is responsive to such variations. Such accurate sensitivity is also achieved by a low flow force spool which rapidly reacts to maintain the required ow. Such sensitivity is also due to the fact that there is no side thrust against the spool or any force normal to the bore surface against the spool so that there is no friction in the spool movement there other than that due to the weight of the spool when the valve is mounted for horizontal movement of the spool.

Another important object is to provide such a demand valve in which variations in inlet pressure will not affect the operation of the valve, the valve having, for this purpose, a balancing piston of the same effective area as the valve head connected to move therewith.

Another important object is to provide such a demand valve which has the required flow capacity to accord modate a high flow rate in a very small unit and Without substantial pressure drop.

Another object is to provide suc-h a demand valve which can be used as a single stage pressure reducer for both liquids and gases from a very high to a very low pressure as from inlet pressures of from 50 to 2000 p.s.i. to an outlet pressure of one-half inch of water.

Another Object is to provide such a demand valve which is self cleaning and does not require a iilter, the working clearances being so small (in the order of millionths of an inch and hence of the same `order as the flow clearances in a sintered filter) as to render a filter unnecessary.

Another object is to provide such a demand valve 3,343,553 Patented Sept. 26, 1Q67 which will meet all standard military requirements, the weight of the spool being very small in relation to its eifective area so as to be both highly sensitive and to have a high ow capacity.

Another object is to provide such a demand valve which is of rugged and simple construction and will stand up under conditions of severe and constant use without getting out of order or requiring repairs.

Other objects and advantages of the invention =will be apparent from the following description 'and drawings in which:

FIG. 1 is a greatly enlarged central vertical section of a demand valve embodying the present invention and showing the same connected with a high pressure oxygen supply line and an outlet line leading, say, to the mask of an aviator, and this section being taken generally on line 1 1, FIG. 3.

FIGS. 2 and 3 are horizontal sections taken on the correspondingly numbered lines on FIG. 1.

FIG. 4 is a modied form of the invention characterized by the demand valve being inverted as compared with FIG. l and by the elimination of the safety pressure spring 44, this spring being rendered unnecessary because the weight of the spool, in the inverted condition, biases the valve to an open position.

Both forms of the valve comprise a cylindrical valve body 10 having a coaxial through bore of varying internal diameter and connected at one end by a line 11 with a source of high pressure oxygen under a pressure of, say, from 50 to 2000 p.s.i., this high pressure supply line being shown as fixed to the end of the valve body 10 by a conventional band 12. At its other end the valve body 10 is shown as connected by a tube 13 with the part to be served, such as the mask (not shown), of an aviator, the demand valve being opened in response to the inhalation of the aviator to admit oxygen to the mask at high altitudes where ambient pressure is below that necessary for breathing requirements.

The valve body 1d as illustrated is greatly enlarged and an adequate demand valve for breathing purposes at high altitudes can be embodied in a cylindrical body 10 which is 1 inch long, has .312 inch outside dia-meter, and weighs about one-half ounce when made of stainless steel, a feature of the invention residing in the capability of mounting the demand valve directly in the oxygen supply line for the aviator.

At the inlet end of the body 1G, the through lbore is of large diameter to provide a cylindrical high pressure inlet chamber 16 and which is shown as terminating in an annular internal shoulder 18 formed by a valve plug bore 19 of reduced diameter. This valve plug bore 19 in turn terminates in an annular internal shoulder 20 formed 'by a piston bore 21 of still further reduced diameter. The outlet end of this piston bore 21 terminates in an enlarged annular channel 22, the outlet side of which continues in a reduced valve seat vbore 23 of the same diameter as the piston bore 2.1. This valve seat .bore 23 leads to an outlet chamber 24 of larger cross sectional size than the valve seat bore 23 which is open at the discharge end of the valve body 10 and :which forms an annular internal shoulder 25 providing a valve seat rim 26 of abrupt cross sectional form. Only this rim 26 immediately surrounding the valve seat bore 23 is used as a valve seat, the valve spool having, in effect, knife edge contact with this rim 26 as will more fully appear.

The valve plug bore 1% and the enlarged channel 22, between and in communication with the piston bore 21 and valve seat bore 23, are connected by an annular series of passages 27 which surround the piston bore 2.1 as best shown in FIGS. 2 and 3. Also a radially extending veut passage 28 connects the end of the piston bore 21, toward the inlet end of the valve body 10, with ambient.

The Valve also includes a fixed plug 30 having a cylindrical body 31 of large diameter press fitted in the valve plug bore 19, a portion 32 of reduced diameter forming an annular channel 33 with the valve plug bore 19 and annular internal shoulder of the valve body, and an end stern 34 of still further reduced diameter forming an annular shoulder 35 abutting the annular internal shoulder 20 of the valve body, the stem 34 extending up into the center of the bore 21. The annular channel 33 is in communication with the annular series of axially extending passages 27 of the valve body and also with a similar series of axially extending passages 36 opening into the enlarged inlet chamber 16 of the valve.

The movable valve member is in the yform of a spool indicated generally at 40' which in the Valve illustrated weighs approximately .006 ounce and is held against endwise displacement by a cross pin 41 in the Valve body extending across the enlarged outlet chamber 24 in close proximity to the internal annular shoulder 25. This spool comprises a cup-shaped enlarged cylindrical piston 42 closely slidingly fitted in the piston bore 21 and having a blind bore 43 facing the inlet end of the valve and housing the stem 34 which forms a guide for a helical compression spring 44 interposed between the blind end of the bore 43 and the annular shoulder 35 of the plug 30. The spool 40 includes an integral stem 45 of reduced diameter contained within the bores 21 and 23 and enlarged internal annular channel 22 and having an enlarged integral valve head 46 at its outboard end. This valve head is in the form of an outwardly extending annular cylindrical flange of the same outside diameter as the valve seat bore 23 and having an abrupt annular shoulder 47 arranged to have knife edge contact with the rim 26, the shoulder immediately surrounding the valve seat bore 23. The stem and head 45, 46 of the spool 40 can have an axial blind bore 48 to decrease the weight of this spool.

In the operation of the valve, it will be assumed that at any altitude ambient pressure in the vent 28 and adjacent end of the piston bore 21 is substantially below the mask pressure contained in the outlet chamber 24 and line 13 leading to the mask. With the mask pressure in the outlet line 13 above ambient, and with lower ambient pressure in the bottom of the piston bore 21 because of the vent 28, the valve head 46 will be held in its closed position illustrated against the bias of the safety pressure spring 44 which biases this valve head to its open position. This is because of the preponderating pressure in the outlet chamber 24 against the end of the valve head 46 as compared with the reduced pressure against the piston 42 forming the opposite end of the spool 40, the effective diameters of the valve head 46 and piston 42 being substantially the same by virtue of the bores 21 and 23 being of substantially the same diameter and the shoulder 47 of this valve head 46 having knife edge contact with the rim 26 of the valve seat bore 23.

The inlet pressure of the oxygen supplied by the line l11 can be of any value and variations and this inlet the outlet of this valve seat bore 23 is equal to the effective area of the piston 42 facing this valve seat bore 23 and hence this inlet pressure is balanced and has no tendency either to open or to close the valve head 46.

When the aviator inhales, he reduces the pressure in the line 13 and outlet end chamber 24 sufliciently to move the valve head 46 away from its knife edge contact with the rim 26 of the shoulder 25. Accordingly, high pressure oxygen from the supply line 11 will flow from the inlet chamber 16 of the valve body via the annular series of axially extending passages 36 into the enlarged internal annular channel 33 and thence through the annular series of axially extending passage 27 into the annular internal enlarged channel 22 and thence from the valve seat bore 23 past the now open valve head 46 into the outlet end chamber 24 of the valve body and line 13 to the mask (not shown) of the aviator. At the end of the inhalation the oxygen pressure in the outlet chamber 24 builds up to the value required to close the valve head 46 and cut off further flow of oxygen. This operation is repeated on each inhalation of the aviator thereby to supply him with oxygen at the required pressure for breathing from a high pressure source.

The form of the invention shown in FIG. 4 is identical with that shown in FIGS. 1-3, except that it is inverted so that the weight of the spool 40 biases the valve head 46 to a normally open position. This permits of the elimination of the safety pressure spring 44 which elimination is the only mechanical difference between the two forms of the invention It will particularly be noted that the full maximum diameter of the spool 40, namely at the outboard end of the valve head 46, is utilized to open the valve and due to the very light weight of this spool, this opening can be effected by a drop in outlet pressure caused by the inhalation of the user even though the oxygen supply is under very high pressure. Even though capable ofV being open in response to slight variations in demand, the flow rate past the separated shoulders or rims 26 and 47 can be very high. The spool 40 is preferably light in Weight to aid the sensitivity of the Valve and since the effective areas of its valve head 46 and piston 42 are equal, variations in inlet pressure have no effect on the action or sensitivity of the valve. In the form of the invention shown in FIG. l, the outlet pressure maintained by the valve is a function of the spring force of the spring 44 and the pressure drop from zero to maximum flow is a -function of its spring rate. Also since the spool 40 is advantageously fitted in the bores 21 and 23 with a tolerance in the order of 20 millionths of an inch, about the same as the flow clearances in a sintered filter, the demand valve is self-cleaning and will not hang up. due to dust particles.

I claim:

A demand valve for supplying pressurized oxygen from an inlet tube to an outlet tube in response to human inhalation demand impressed on the outlet end of said outlet tube, comprising (A) a one-piece valve body having (a) a through bore concentric with a single axis and formed to provide, successively (l) a cylindrical outlet chamber of relatively large diameter at the end of said through bore opening into said outlet tube,

(2) a concentric cylindrical valve seat bore of smaller cross sectional size than said outlet chamber and forming a direct continuation thereof with a valve seat rim of abrupt cross section separating said valve seat bore from said outlet chamber,

(3) a concentric channel of larger diameter than and forming a direct continuation of said valve seat bore,

(4) a concentric cylindrical piston bore of substantially the same diameter as said valve seat bore and forming direct continuation of said channel,

(5) a concentric cylindrical plug seating bore of at least the same diameter and forming a direct continuation of said piston bore, and

(6) a cylindrical inlet chamber 0f at least the same diameter and forming a direct continuation of said plug seating bore and opening into said inlet tube,

(b) at least one passageway connecting said cylindrical inlet chamber and said channel, and

(c) a passage supplying reference pressure to the end of said piston bore remote from said channel,

(B) a cylindrical plug press tted in said plug seating bore closing the end of said piston bore adjacent said passage and having at least one passage connecting said cylindrical inlet chamber with said passageway,

References Cited UNITED STATES PATENTS 556,023 3/1896 Pew a 137-538 X 1,698,567 1/1929 Small 137-539 X 2,590,622 3/1952 Huber 137-505.13 X

WILLIAM F. ODEA, Primary Examiner.

ISADOR WEIL, Examiner.

R. GERARD, Assistant Examiner. 

